Wetting is the ability of a liquid to maintain contact with a solid surface. Liquid that wets a surface spreads out over that surface. Liquid that does not wet a surface will minimize contact with that surface and become a more spherical droplet.
Surface roughness affects the wetting behavior. If surfaces are “non-wetting” then surface roughness tends to make the surface less wetting and more non-wetting. If the surface is “wetting” then roughness tends to make it more wetting.
Chemical treatments are used on surfaces to change wetting properties. Rain-X® is an example of a hydrophobic surface treatment consisting of polymer molecules that stick to glass and repel water. A small amount of Rain-X® by 3M Corporation (St. Paul, Minn.) applied to a windshield facilitates the “de-wetting” of the windshield by causing water to “ball-up” due to the large contact angle between water and a Rain-X® coated surface. Chemical treatments are used as sizing and coating for paper and fabric—woven and non-woven to control the way these materials interact with fluids from diapers to ink jet printer paper. Scotchgard®, also by 3M Corporation, creates a hydrophobic surface on fabrics. Modifying the wettability of surfaces chemically is well-known and widely practiced.
Recent advances in nanotechnology, particularly biomimicry, have renewed interest in how structure can modify surface properties. From the self-cleaning surface of plants, coined the “Lotus Leaf Effect,” to propulsion in water walking insects; nature uses chemistry AND structure to control interaction with fluids. “Biomimetic modification of surface properties,” had over 100,000 hits on Google Scholar in January, 2016.
Studies have shown that nanofibers have an ability to form structures that to a degree mimic those present in nature. The unique properties of the nanofibers allow the creation of fibers that are superhydrophobic or superhydrophilic, essentially enhancing the properties of the bulk material. Nanofibers for prior art surface wettability modification are commonly made by electrospinning, a method that requires the use of high voltages and a flowing polymer solution containing solvents that evaporate during production. Ensor, et al. in U.S. Pat. No. 8,652,229 describe methods for electrospinning nanofibers for forming filter elements. In the methods described, the electrospinning process requires electrical potentials in the 25 kV to 30 kV range and the close control of several process parameters. The rates of nanofiber production are low in the examples given. It is not an environmentally friendly process due to the solvents required and is not easily scalable to produce the large quantities required for commercial products, particularly consumer products.
Nanofibers produced by electrospinning are long and continuous with few fiber ends created. The orientation is random and the fibers are not bonded to an underlying surface. This is in contrast to nanofibers occurring in nature that are generally highly ordered, are integral with an underlying surface, and have an abundance of fiber ends.